The synchronization of clocks and timing devices between the satellites and receivers is critical to obtaining an accurate reading. If the clocks are even a little off your receiver could be off by a significant distance. The problem that arises here is that no clocks keep time perfectly. After a period of time different clocks will show different times from each other. Atomic clocks are the most precise time measurements that we have but at $50,000-$100,000 each the cost of putting one of those in a receiver instantly puts GPS receivers outside the budget of most individuals. The solution was to install cheaper quartz clocks in the receivers and program them to reset themselves based on information received from three of four satellites. With this method GPS receivers are able to retain the time accuracy required for an accurate reading without being overly expensive.

The synchronization of clocks and timing devices between the satellites and receivers is critical to obtaining an accurate reading. If the clocks are even a little off your receiver could be off by a significant distance. The problem that arises here is that no clocks keep time perfectly. After a period of time different clocks will show different times from each other. Atomic clocks are the most precise time measurements that we have but at $50,000-$100,000 each the cost of putting one of those in a receiver instantly puts GPS receivers outside the budget of most individuals. The solution was to install cheaper quartz clocks in the receivers and program them to reset themselves based on information received from three of four satellites. With this method GPS receivers are able to retain the time accuracy required for an accurate reading without being overly expensive.

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The positioning of the satellites can also cause problems due to their geometry. Even though the satellite positions are monitored, they can not be watched every second. Slight positioning errors, or "ephemeris", between monitoring times can cause errors. These errors can be compounded by the principle of "Geometric Dilution of Precision." Since there are more available satellites than necessary to a receiver normally, the receiver picks few and ignores the rest. However, if the receiver picks satellites that are posistioned too close together, then the signals will cross at very shallow angles, which increases the margin of error in the position of the receiver. To eliviate this problem, receivers are being equipped with software that helps them better pick satellites that will have signals cross close to 90 degree angles, which minimizes the margin of error due to geometry of the satellites.

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The positioning of the satellites can also cause problems due to their geometry. Even though the satellite positions are monitored, they can not be watched every second. Slight positioning errors, or "ephemeris", between monitoring times can cause errors. These errors can be compounded by the principle of "Geometric Dilution of Precision." Since there are more available satellites than necessary to a receiver normally, the receiver picks few and ignores the rest. However, if the receiver picks satellites that are positioned too close together, then the signals will cross at very shallow angles, which increases the margin of error in the position of the receiver. To alleviates this problem, receivers are being equipped with software that helps them better pick satellites that will have signals cross close to 90 degree angles, which minimizes the margin of error due to geometry of the satellites.

The last problem addressed here is the problem of judging the distance. The distance from the receiver to the satellite is based on the signal traveling at the speed of light in a straight line. However that is often not the case. When that signal enters earth’s atmosphere it doesn’t maintain the speed of light but actually slows down a bit. To add to the confusion, if you are in a city with tall buildings around the signal can bounce off of the buildings before getting to your receiver adding a significant margin of error. To accommodate for this, a secondary checking system was set up and called the Differential GPS. Differential GPS works by setting up a stationary receiver antenna on the earth and using that as a check against the satellite. A GPS receiver knows its own position on the earth. It uses measurements from the satellites to calculate inaccuracies in the satellite reading and then provide the correction data to other receivers in the area.

The last problem addressed here is the problem of judging the distance. The distance from the receiver to the satellite is based on the signal traveling at the speed of light in a straight line. However that is often not the case. When that signal enters earth’s atmosphere it doesn’t maintain the speed of light but actually slows down a bit. To add to the confusion, if you are in a city with tall buildings around the signal can bounce off of the buildings before getting to your receiver adding a significant margin of error. To accommodate for this, a secondary checking system was set up and called the Differential GPS. Differential GPS works by setting up a stationary receiver antenna on the earth and using that as a check against the satellite. A GPS receiver knows its own position on the earth. It uses measurements from the satellites to calculate inaccuracies in the satellite reading and then provide the correction data to other receivers in the area.

Introduction

DeLorme Earthmate PN-20 GPS Source: Amazon.com

The DeLorme Earthmate PN-20 GPS receiver helps navigate the globe using a web of satellites. The idea of world-wide positioning technology took some time to develop into the system we have today. It was first based on radio navigation systems from WWII. The idea was also propelled further following the Soviet Union's launch of Sputnik in 1957. The first GPS satellite was launched in 1978 by the United States Department of Defense. The Department of Defense developed this technology for military use, and named the program NAVSTAR GPS. However, in 1983 after a Soviet aircraft shot down a civilian plane, President Reagan announced that the NAVSTAR GPS network would be open for public use upon it's completion. The 24th satellite was launched in 1994, and by April 1995 the system was fully operational. There are several other global navigation satellite systems being developed today, including the Russian GLONASS network, the European Galileo positioning system, as well as the Chinese COMPASS navigation system. In 1998, a plan to improve the accuracy and reliability of the NAVSTAR GPS network was announced. In 2004, the A-GPS (Assisted GPS) was introduced to enhance the performance further. The A-GPS came hand in hand with a FCC mandate which required that all cell phones could be tracked using GPS and located by Emergency Call Dispatchers.

The sole application of GPS is not only for the use of the government and cell phone tracking. Presently, GPS is used for countless applications, including military use, mapping and surveying, emergency cell phone and vehicle tracking, as well as personal devices like the DeLorme Earthmate PN-20

Our group is going to focus on the various applications of the GPS network. The group consists of Terry Alexander, Tim Blackwell, Ben Greene, Tyler Weber, Mike Wexler, and John Wilson.

Error Correction

Though the theory for the calculation of a point with GPS is sound there are several variables in the real world that can cause inaccuracies in the readings of GPS data. The clocks in the satellites or the receiver may drift away from “true time”, the thickness of the atmosphere by the receiver, signals from the satellite bouncing off of buildings or skyscrapers and other tall objects can cause inaccurate readings from GPS equipment.

The synchronization of clocks and timing devices between the satellites and receivers is critical to obtaining an accurate reading. If the clocks are even a little off your receiver could be off by a significant distance. The problem that arises here is that no clocks keep time perfectly. After a period of time different clocks will show different times from each other. Atomic clocks are the most precise time measurements that we have but at $50,000-$100,000 each the cost of putting one of those in a receiver instantly puts GPS receivers outside the budget of most individuals. The solution was to install cheaper quartz clocks in the receivers and program them to reset themselves based on information received from three of four satellites. With this method GPS receivers are able to retain the time accuracy required for an accurate reading without being overly expensive.

The positioning of the satellites can also cause problems due to their geometry. Even though the satellite positions are monitored, they can not be watched every second. Slight positioning errors, or "ephemeris", between monitoring times can cause errors. These errors can be compounded by the principle of "Geometric Dilution of Precision." Since there are more available satellites than necessary to a receiver normally, the receiver picks few and ignores the rest. However, if the receiver picks satellites that are positioned too close together, then the signals will cross at very shallow angles, which increases the margin of error in the position of the receiver. To alleviates this problem, receivers are being equipped with software that helps them better pick satellites that will have signals cross close to 90 degree angles, which minimizes the margin of error due to geometry of the satellites.

The last problem addressed here is the problem of judging the distance. The distance from the receiver to the satellite is based on the signal traveling at the speed of light in a straight line. However that is often not the case. When that signal enters earth’s atmosphere it doesn’t maintain the speed of light but actually slows down a bit. To add to the confusion, if you are in a city with tall buildings around the signal can bounce off of the buildings before getting to your receiver adding a significant margin of error. To accommodate for this, a secondary checking system was set up and called the Differential GPS. Differential GPS works by setting up a stationary receiver antenna on the earth and using that as a check against the satellite. A GPS receiver knows its own position on the earth. It uses measurements from the satellites to calculate inaccuracies in the satellite reading and then provide the correction data to other receivers in the area.

Public Safety and Disaster Relief using GPS

The Global Positioning System (GPS) provides information that is critical to disaster relief teams and public safety personnel in order to protect life and reduce property loss. GPS has played a vital role in relief efforts for global disasters such as the tsunami that struck in the Indian Ocean region in 2004, Hurricanes Katrina and Rita that wreaked havoc in the Gulf of Mexico in 2005, and the Pakistan-India earthquake in 2005.

Another area of disaster relief that may not be commonly thought of is the management of wildfires. To contain and manage forest fires, aircraft combine GPS with infrared scanners to identify fire boundaries and “hot spots.” Within minutes, fire maps are transmitted to a portable field computer at the firefighters’ camp. Armed with this information, firefighters have a greater chance of winning the battle against the blaze.

GPS is playing an increasingly prominent role in helping scientists to anticipate earthquakes. Using the precise position information provided by GPS, scientists can study how strain builds up slowly over time in an attempt to characterize, and in the future perhaps anticipate, earthquakes.

GPS has given managers a quantum leap forward in efficient operation of their emergency response teams. The ability to effectively identify and view the location of police, fire, rescue, and individual vehicles or boats, and how their location relates to an entire network of transportation systems in a geographic area, has resulted in a whole new way of doing business. Location information provided by GPS, coupled with automation, reduces delay in the dispatch of emergency services.

The FCC now requires that all cell phones be equipped with a GPS device. This helps emergency call dispatchers locate where the call is coming from. With this information, victim's that are unable to give their whereabouts will still be able to be located by emergency services.

The modernization of GPS will further facilitate disaster relief and public safety services. GPS modernization translates to more lives saved and faster recovery for victims of global tragedies.

Surveying and Mapping with GPS

Using the near pinpoint accuracy provided by the Global Positioning System (GPS) with ground augmentations, highly accurate surveying and mapping results can be rapidly obtained, thereby significantly reducing the amount of equipment and labor hours that are normally required of other conventional surveying and mapping techniques. Today it is possible for a single surveyor to accomplish in one day what used to take weeks with an entire team. GPS is unaffected by rain, wind, or reduced sunlight, and is rapidly being adopted by professional surveyors and mapping personnel throughout the world.

Throughout the world, government agencies, scientific organizations, and commercial operations are using the surveys and maps deriving from GPS for timely decision-making and wiser use of resources. Any organization or agency that requires accurate location information can benefit from the efficiency and productivity provided by the positioning capability of GPS.

Unlike traditional techniques, GPS surveying is not bound by constraints such as line-of-sight visibility between reference stations. Also, the spacing between stations can be increased. The increased flexibility of GPS also permits survey stations to be established at easily accessible sites rather than being confined to hilltops as previously required.

Remote GPS systems may be carried by one person in a backpack, mounted on the roof of an automobile, or fastened atop an all-terrain vehicle to permit rapid and accurate field data collection. With a GPS radio communication link, real-time, continuous centimeter-level accuracy makes possible a productivity level that is virtually unattainable using optical survey instruments.

Recreational GPS Use

Recreational GPS Use

GPS has eliminated many of the hazards associated with common recreational activities by providing a capability to determine a precise location. GPS receivers have also broadened the scope and enjoyment of outdoor activities by simplifying many of the traditional problems, such as staying on the “correct trail” or returning to the best fishing spot.

Outdoor exploration carries with it many intrinsic dangers, one of the most important of which is the potential for getting lost in unfamiliar or unsafe territory. Hikers, bicyclists, and outdoor adventurers are increasingly relying on GPS instead of traditional paper maps, compasses, or landmarks. Paper maps are often outdated, and compasses and landmarks may not provide the precise location information necessary to avoid venturing into unfamiliar areas. In addition, darkness and adverse weather conditions may also contribute to imprecise navigation results.

GPS technology coupled with electronic mapping has helped to overcome much of the traditional hardships associated with unbounded exploration. GPS handsets allow users to safely traverse trails with the confidence of knowing precisely where they are at all times, as well as how to return to their starting point. One of the benefits is the ability to record and return to waypoints.

Golfers use GPS to measure precise distances within the course and improve their game. Other applications include skiing, as well as recreational aviation and boating.

GPS technology has generated entirely new sports and outdoor activities. An example of this is geocaching, a sport which rolls a pleasurable day’s outing and a treasure hunt into one. Another new sport is geodashing, a cross-country race to a predefined GPS coordinate.

Geocaching

Overview

Geocaching is a sport where a cache is left in a location anywhere in the world, and its coordinates are uploaded to any of a number of geocaching websites. A GPS unit is used to locate the cache by entering the coordinates as the destination waypoint. A cache is usually a small waterproof box with a prize, generally not valuable and a logbook to see how many others have found that cache. The participants are asked to put something new in the box, write some information in the logbook, at least their name and the date they found the cache. Logbooks also often contain information about the area, nearby attractions or even jokes. Geocaching etiquette states that if you get some useful information from the logbook; try to leave some useful information.

General Rules

1. Take something from the cache
2. Leave something in the cache
3. Write about it in the logbook

Variations on the Game

Offset caches – The coordinates lead to a monument or another benchmark, where the hunter must look for new clues, or follow directions found on a cashing website.

Multicaches- The cache has the coordinates or directions to another cache, until the hunter reaches the final cache.

Virtual caches - A cache is an existing landmark. The hunter must answer a question from the landmark to the cache owner to get the prize.

Moving caches – The hunter moves the cache to a new location and updates the website after finding it

Caches can be hidden anywhere on the planet, with varying difficulty. For example, some caches can only be reached by rock climbing up a sheer face or diving underwater with scuba gear. Others involve hiking miles from the nearest road. There are over 540,000 geocaches on all seven continents.

Geocaching Policy

Geocaching websites often have a policy to protect hunters and their cashes. Common policies include warnings about geocaching on National park lands and privately owned land. The policies also refer to treading lightly on environmentally sensitive and archaeologically significant locations. Geocachers are also warned to avoid looking suspicious as many hunters have been questioned by police especially when in a location where security is essential.

Terrestrial Vehicle use of GPS

It is common today to see GPS receivers built into new vehicles or to see an individual unit installed in older vehicles. By introducing this system, the driver will be provided with navigation, which may be linked to real-time information systems reducing travel time and fuel consumption. Provided that the trip information was programmed prior to leaving, GPS navigation will increase road safety as drivers who are unfamiliar to a region will be able to reach their destination without having to remove their eyes from the road.

Vehicle tracking has been a new feature introduced to industries and to the public. Commercial industries can use GPS to locate a shipment of packages, the speed of the driver, and the estimated time of arrival down to the minute. Law enforcement in Los Angeles are testing a device that deploys a GPS receiver onto a fleeing vehicle to track them instead of entering a potentially high speed and/or fatal pursuit. Public uses can include a parent tracking the location of children driving a tagged vehicle with the additional ability to check where the car stopped and for how long, the maximum speed, and average speed of the vehicle.

The future uses of GPS will undoubtedly grow as the US government is designing the Intelligent Transportation System (ITS). Automakers are using GPS in addition with other technologies to design cars that have automatic driving systems built in, which will be able to drive a vehicle to a set location.

Aviation with GPS

With the introduction of GPS and the numerous advances made in increasing accuracy, aviation has benefited greatly. The GPS system alone provides useful information allowing pilots to fly in more efficient routes in a safe manner. There are two augmentations have provided airports with smoother operation and safety, these are the Wide Area Augmentation System (WAAS) and the Local Area Augmentation System (LAAS).

WAAS is a satellite based augmentation to GPA that covers the entire United States airspace and corrects for errors that occur in standard GPS signals. These signals have an accuracy of 7 meters as opposed to the GPS accuracy of 100 meters and are useful in aiding pilots in landing and enroute. Pilots will be able to plot courses that are more direct because the paths do not require ground surface infrastructure.

LAAS is a system that assists GPS in a specific location, such as an airport runway, and provides much better accuracy on the local level by using ground equipment. If installed at airports, regulators will be able to reduce the distance requirements imposed on aircraft, allowing for greater number of flights. Using the LAAS, a pilot will have the ability to land a plane in conditions of zero visibility, although this has not yet been approved by the Federal Aviation Administration (FAA) for such use.

Utilizing these two augmentations, there are possibilities for shorter flight times, greater capacity, reduced maintenance costs, and safer flights from takeoff gate to landing gate.

Military GPS Use

Military GPS Use

Along with civilian uses, GPS has multiple military uses. The most common use of GPS within the military is for the guidance of bombs and missiles. The only method of bombing before the development of GPS was to drop a high volume of bombs in order to hit the target. This method was costly in both materials used and especially in civilian collateral damage and casualties. With the use of GPS missiles and bombs can be guided directly onto a target. Modern missiles use multichannel GPS receivers to constantly update its position relative to its target. This ensures the highest level of accuracy possible in order to minimize collateral damages and civilian casualties while accomplishing the mission.

Another use of GPS within the military is in navigation. Personal GPS systems can allow operations to be undertaken during the night while still maintaining a high navigational standard. It can also be used to track a soldier in the event of a rescue mission being required. Also, it can be used on a larger scale as it can provide near instant feedback regarding troop location and deployment. This can be used by officers running an offensive to efficiently coordinate their troops in an attack.

Maritime GPS Use

An area where GPS is rapidly gaining use is at sea. In the shifting tides and currents of the earth’s waterways, it is vital for a ship’s captain to be able to accurately determine his position, bearing, and speed. This is important to ensure that the ship maintains its course and reaches port in the fastest possible manner. Any delays at sea would cost a commercial shipping company large sums of money. GPS is also used to ensure the safety of vessels at sea, and especially as they exit or enter ports. Along with being able to track and avoid other vessels in the area, GPS is used to steer around underwater obstacles. Barrier reefs and other underwater obstacles can be mapped and placed onto GPS systems so that ship captains can successfully steer around these dangerous objects. GPS can also be used to place buoys and other maritime equipment to ensure it is accurately placed.